Connexins (Cxs) are membrane proteins constituting the gap junctions (GJs). The major function of GJs is to provide a regulated conduit for intercellular ionic, electrical and biochemical (e.g., nutrients and signaling molecules) couplings. Genetic studies have linked more than 100 mutations in the Cx26 gene to a large proportion of prelingual nonsyndromic deafness. Despite the importance of GJs in hearing as revealed by genetic studies, we know very little about their functional role in the cochlea. One major reason is the lack of appropriate animal models based on which human hereditary deafness caused by various types of Cx mutations could be studied. Our long-term goal is to understand the function of GJ channels in the cochlea at the molecular level. We hypothesize that the molecular mechanisms underlying pathological changes of large truncation mutations and point mutations of Cx26 are markedly different. We will use genetic engineering techniques to create mouse models that are both informative in revealing the molecular function of cochlear GJs and in helping us understand cochlear pathologies caused by various types of human Cx26 mutations. Using the Cre-loxP mediated conditional gene targeting method, we will create four lines of mouse models representing the following four types of human Cx26 mutations as revealed from in vitro studies: (1) mutations that cause a selective loss of biochemical permeability (e.g., V84L); (2) mutations that alter the Ca++ binding affinity to Cx26 hemichannels, such that hemichannels are leaky at physiological concentrations of Ca++ (e.g., G45E); (3) mutations that cause a selective loss of GJ whole channel functions, but the hemichannel function is largely unchanged (e.g., R75W); (4) total loss of GJ- mediated intercellular communications (e.g., D179N). We will then examine the morphological and functional changes in the cochleae of the four lines of genetically modified mice. The availability of these mouse models will greatly facilitate investigations into the mechanism of the most common form of congenital hearing impairment at the molecular level. The knowledge gained should advance our understanding of the functional roles of GJs in the cochlea as well as help designing treatment strategies for a large portion of hereditary deafness patients. Genetic studies have linked more than 100 mutations in the connexin genes to about half of all cases of prelingual deafness. The focus of this project is to establish appropriate animal models based on which human hereditary deafness caused by various types of Cx mutations could be studied. The availability of these mouse models will greatly facilitate investigations into the mechanism of most common form of congenital hearing impairment at the molecular level. The knowledge gained should help us design better treatment strategies for a large portion of hereditary deafness patients. [unreadable] [unreadable] [unreadable]